Moving optical beams is required for a number of different applications, including scanning devices, imaging devices, illumination devices, optical switching devices, and optical analytical devices among others. In a number of prior such devices this movement of the optical beams has been effected by moving a flexible optical fiber.
For example one device and method for movement of an optical fiber is disclosed in U.S. Pat. No. 5,727,098. This reference discloses a scanning optical fiber system in which the fiber is fixed at a first end, and may flex at a second end. At this second end a magnetic material is positioned. A plurality of electromagnets are arranged to produce a variable magnetic field that interacts with the magnets to deflect the optical fiber in a predetermined scanning pattern. In addition, a feedback device detects the position of the fiber and provides information on the deflection of the second end of the fiber to achieve the required scan patterns. The feedback device may be a hall effect detector, a proximity sensor, a strain gauge that actuates a transducer, a magnetic impedance detector, or similar device.
A second device for moving an optical fiber is disclosed in U.S. Pat. No. 6,845,190 in which a resonating optical conduit (for example a cantilevered light guide) is used with a specialized control. The controller induces a phase signal source that produces a reference signal and a phase control coupled to a sensor to receive a position signal and a reference signal. An amplitude controller is also used that includes an amplitude reference source and an amplitude control coupled to a sensor to receive a position signal. The resulting output from the phase control and the amplitude control are combined to control the drive of the resonating optical conduit. These controllers can utilize both open loop and closed loop controllers.
Another alternative for moving an optical fiber is to create a “bimorph”, a physically elongate fiber including an optical fiber joined to an expandable/contractible structure to form a single fiber. For example, U.S. Pat. No. 6,091,067 discloses a cantilever-mounted optical fiber within a micro electro-mechanical motor. The fiber is flanked by two piezoelectric elements to form a unitary structure, a bimorph. The piezoelectric elements may be excited to cause the structure to rapidly bend, producing a line scan. U.S. Pat. Nos. 4,520,570; 6,501,210 and others also disclose variations of the bimorph technology.
U.S. Pat. No. 6,046,720 discloses another alternative device in which an optical fiber is scanned, such as in a raster pattern. In this reference a resonant cantilever, driven by an electromagnetic drive circuit or piezoelectric drive, moves the fiber.
U.S. Patent App. No. 2002/0064341 discloses a scanning optical conduit that has a first fixed end and a second, tapering end. The tapered end may include a “hinge”, i.e., a location where the diameter of the fiber narrows, to enhance movement. A mechanical vibratory resonator at the tip of the conduit may move in a one or two-dimensional scan pattern at a selected amplitude and frequency. A microlens may be affixed to the top of the optical fiber.
U.S. Pat. No. 5,808,472 discloses a device and method of positioning an optical fiber and determining the position of the optical fiber. A capacitance member on the free end of the optical fiber responds to a generated electric field.
These prior art references all provide various tools for moving an optical fiber to produce a scan of a beam of light. However, accurate and rapid movement of the beam has proved elusive for a variety of reasons. First, an optical fiber section has a characteristic frequency at which the fiber will seek to move. Moving the optical fiber at other frequencies has proved challenging. Second, the scanning provided in the prior art references generally is done along a single axis. In references in which the scanning is along two axes, it is difficult to move the fiber in a manner in which the fiber moves along just a single axis first, then the second axis.
There are six degrees of freedom associated with the unique determination of the position of the end of a conduit. This includes three translational degrees of freedom (x,y,z axis) and three rotational degrees of freedom (yaw, pitch and roll). Active conduit control of three or more degrees of freedom has not been reported to date.
In order to move the conduit it is typically required to induce the desired motion in a number, L, of degrees of freedom, while restricting the motion in a number, M, of degrees of freedom where M plus L equals 6. Active restriction of undesired degrees of freedom of motion has not been reported to date.
Another consideration in the precise sub-micron movements of structures is the interaction between the operator of a sub-micron differential micrometer and the structure. The act of touching the micrometer deforms the structure more than a sub-micron level adjustment. In practice, however, a skilled operator can compensate somewhat for these difficulties.
In a number of commercially available mechanical structures a latching mechanism is provided as a separate adjustment from the micrometer. For example this may be a screw that may be tightened up against the micrometer to prevent the micrometer from inadvertent turning. However, typically latching the micrometer disturbs the structures' position. Again a skilled operator can compensate somewhat for these difficulties.
Regarding the sub-micron level performance of flexure based structures the latch does not prevent what is known as creep or the slow deformation of the entire structure that may be caused by the loading forces required to bend the flexure structure.